System and method of transfer printing an organic semiconductor

ABSTRACT

The present invention provides a substrate having thereon a patterned small molecule organic semiconductor layer. The present invention also provides a method and a system for producing a substrate having thereon a patterned small molecule organic semiconductor layer. The substrate having thereon a patterned small molecule organic semiconductor layer is produced by exposing a donor substrate having thereon a small molecule organic semiconductor layer to energy to cause the thermal transfer of a small organic molecule onto an acceptor substrate.

[0001] This application is related to commonly-owned U.S. Applicationentitled “The Use of an Energy Source to Convert Precursors intoPatterned Semiconductors,” Ser. No. ______, filed herewith on the sameday, cross-referenced and incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to substrates having thereon apatterned small molecule organic semiconductor layer. The invention alsorelates to a method and a system for the production of such substrateshaving patterned small molecule organic semiconductor layers thereon.The patterned small molecule organic semiconductor layer is formed bythe thermal transfer of a small molecule organic semiconductor or itsprecursor from a donor substrate to an acceptor substrate. Moreparticularly the present invention relates to a substrate having thereona patterned pentacene semiconductor layer.

[0004] 2. Description of the Prior Art

[0005] The concept of transfer printing of inks and various metals isone that has been known for some time. The general idea involves asubstance adhering or affixed to a first surface to be transferred to asecond surface with or without direct physical contact between the twosurfaces. This type of transfer is well known in non-impact printing oftext and also used for transfer of various metals from a first surfaceto a second surface, usually by way of local pulsed heating of the donorsurface. The present invention utilizes preferably a flexible substrateor ribbon or other donor substrates (not necessarily flexible) whichcontain a small molecule organic semiconducting compound or itsprecursor that can be locally heated resulting in a transfer, likely bysublimation, of the small molecule organic semiconducting or precursormaterial from the donor surface resulting in adhesion of the organicsemiconductor onto a second or acceptor surface. The transfer ofmaterial can be used to define a localized pattern on the acceptorsubstrate, for example a material that can be used to create a componentof a semiconducting device. When the heating method utilizes a focusedlaser beam, either incident on the semiconducting material or precursorof a small molecule semiconductor such as pentacene, a very narrow andwell defined transfer can be achieved to define a part of asemiconducting device, for example the channel of a field effecttransistor (FET) or various other semiconducting devices.

[0006] Non-impact transfer printing has been used for a variety ofapplications for a number of years. This form of printing can be dividedinto two categories; first, one in which there is no contact between thefirst surface of the donor substrate from which material is transferredand the first surface receiving the material; and second, one in whichthe two surfaces are in contact but in which there is no impact toimpart the material from the first surface of the donor to the firstsurface of the acceptor. Examples of these types of material transfersare well known in the literature. The transfer of material from a donorsurface to an acceptor surface where the acceptor surface may have beenpreviously chemically treated to cause a chemical reaction with thetransferred material has been described extensively. For example, inkjet type printers for printing semiconductors and other components ofsemiconductor devices have been known for some time and are describedagain most recently in U.S. 2002/0053320 A1.

[0007] U.S. Pat. No. 6,344,660 describes impact printing which involvescontact between a first and second substrate, wherein the firstsubstrate carries ink or some metal that is to be transferred to thesecond substrate by local heating, stamping, or spin coating.

[0008] When melting is used to transfer material, the source of heat maybe a focused laser beam incident on the donor substrate, with a portionof the laser or other energy beam absorbed by the first surface whichmay be a ribbon. Alternatively, the ribbon may contain an electricallyconducting stripe which can be used for localized printing due to thecontact of a high resistance element between the contact point on theribbon and the electrically conducting stripe in which case this form ofheating takes the place of the laser to cause the melting and transferof the material. Print heads that heat the ribbon in one or more placessimultaneously are also well known to achieve thermal transfer.

[0009] However, there is no prior art known to us in whichsemiconducting materials are transferred to a second substrate in acrystalline form. In general, to transfer a semiconductor from onesurface to a second surface has been achieved by the melting of thematerial which then is transferred by vaporization from the molten stateto a second substrate resulting in an amorphous film. In general, thistechnique has been widely used in the processing of electroluminescentdevices but without the use of a precursor that includes a small organicsemiconducting molecule.

[0010] It has recently been discovered that small organic semiconductingmolecules, such as pentacene, can be thermally transferred from certainsubstrates (donor substrate) to a second substrate (acceptor substrate)using localized heating. This results in a type of small moleculedeposition using energy to provide the thermal energy for the transfer.This type of transfer can be made in a partial vacuum. In more recentexperiments it has been found that intimate contact between the donorsubstrate (containing a pre-deposited small molecule organicsemiconductor layer of either the small organic molecule itself or aprecursor to that small molecule) and the acceptor substrate yieldextremely fine thermally transferred patterns of the small organicmolecule onto the acceptor substrate using a focused laser beam. It hasbeen found that the transfer can take place in an ambient atmospheresince the contact between donor and acceptor are sufficiently close toone another that very little, if any of the atmosphere is trappedbetween the contacting substrates nor can the ambient air enter betweenthe acceptor and donor. This type of intimate contact also precludes thepossibility of any substantial contamination of the transferred organic(e. g. pentacene) from the outside ambient.

[0011] Thin-film transistors and other electronic devices using organicsemiconductors, such as pentacene, are emerging as alternatives toestablished methods using amorphous silicon (α-Si:H) as thesemiconductor.

[0012] A variety of organic compounds have been proposed and tested assemiconducting materials for TFT devices. For example, among thep-channel (hole transport) materials that have been characterized arethiophene oligomers proposed as organic semiconductor material for TFTin Garnier, F., et al., “Structural basis for high carrier mobility inconjugated oligomers” Synth. Meth., Vol. 45, p. 163 (1991), andphthalocyanines described in Bao, Z., et al., “Organic Filed-effecttransistors with high mobility based on copper phthalocyanine” Appl.Phys. Lett., Vol. 69, p. 3066 (1996). Pentacene, which is a member ofpoly(acene) compounds has been proposed as an organic semiconductormaterial in Lin et al. IEEE 54th Annual Device Research Conference,1996, pages 2136-2139, and Dimitrakopoulos et al., J. Appl. Phys., 80(4), 1996, pages 2501-2507.

[0013] Some soluble organic compounds have also been characterized asorganic semiconducting materials. For example poly(3-alkylthiophene)described in Bao, Z., et al., “Soluble and Processable regioregularpoly(3-hexylthiophene) for thin film field-effect transistorsapplication with high mobility” Appl. Phys. Lett., Vol. 69, page 4108(1996).

[0014] An attractive material would have a high carrier mobility whichis close to that of amorphous silicon (0.1-1 cm².V⁻¹.s⁻¹), with a veryhigh on/off ratio (>10⁵). For an organic material to replace amorphoussilicon would have not only the electrical properties cited above butalso should be processable from solution so that it could becomecommercially attractive.

[0015] Among the organic compounds which have been studied assemiconductors, only regioregular poly(3-hexylthiophene) is readilysoluble in organic solvents and thin films of this compound have beenprocessed from solution for construction of TFTs. The drawback for thiscompound is that it has relatively low (5×10⁻² cm².V⁻¹.s.⁻¹) carriermobility and even much less satisfactory on/off ratio of less than 100.In addition, because thin films of this polymer are not stable in airand its field-effect characteristics deteriorate on exposure to air, itsapplication as semiconductor becomes less desirable.

[0016] The best performance as a semiconductor among organic materialsto date has been achieved by thin films of pentacene deposited underhigh vacuum and temperature as reported by Dimitrakopoulos et al., inU.S. Pat. Nos. 5,946,511; 5,981,970 and 6,207,472 and other publicationsby Brown et al., J. Appl. Phys. 80(4), 1996, pages 2136-2139 andDimitrakopoulos et al., J. Appl. Phys. 80(4), pages 2501-2507.

[0017] Recently, thin-film transistors on plastic substrates usingevaporated films of pentacene as the p-channel carrier with mobility of1.7 cm².V⁻¹.s.⁻¹ and an on/off ratio of 10⁸ have been reported by Jaksonet al., in Solid State Technology, Vol. 43 (3), 2000, pages 63-77.

[0018] Thin films of pentacene are very stable in air and even moderatetemperatures and as far as performance is concerned, pentacene isprobably the most attractive organic material to date to replaceamorphous silicon.

[0019] The drawback of pentacene is that it is insoluble in commonorganic solvents and can only be deposited as a thin film by expensivehigh vacuum and temperature techniques.

[0020] There has been very little effort for the synthesis of solublepentacene derivatives and the only example of soluble pentacene is byMuellen, K. et al., “A soluble pentacene precursor: Synthesis,solid-state conversion into pentacene and application in a field-effecttransistor,” Adv. Mat. 11(6), p. 480 (1999), in which a precursor ofpentacene is synthesized by a tedious multi-step synthetic approach. Thederivative, which is soluble in organic compounds and can be processedfrom solution, is converted back to pentacene by heating at moderate tohigh temperatures (140-200° C.).

[0021] The drawback for using this compound as a pentacene precursor isthat due to the multi-step synthesis (more than 9 steps), itspreparation, especially in large scale is impractical. In addition, itsconversion to pentacene occurs at a relatively high temperature whichprevents the use of most plastics as substrates.

[0022] Commonly owned and copending application entitled “HeteroDiels-Alder Adducts of Pentacene as Soluble Precursors of Pentacene,”Ser. No. ______, Filed on Nov. 20, 2002, IBM ref: YOR920020160US1,contents of which are incorporated herein by reference, describes aspecially prepared pentacene precursor that can be spun, dipped, orsprayed onto a substrate from which a small molecule organicsemiconductor can result from simple thermal processing of theprecursor. The precursor, after application to a substrate, is thenallowed to dry. Upon heating the substrate (upon which the driedprecursor film resides) on a hot plate at temperatures of 200° C. orless for several minutes or less the precursor has been shown totransform into a pure small molecule organic semiconductor, such aspentacene. Commonly owned and copending application entitled “Thin FilmTransistors Using Solution Processed Pentacene Precursor as OrganicSemiconductor,” Ser. No. ______, filed on Nov. 20, 2002, IBM ref: YOR920020161US1, contents of which are incorporated herein by reference,describes the application of a solution processed polycyclic aromaticcompound precursors as an organic semiconducting material in thin filmtransistors.

[0023] The present invention describes a method and a system forproducing a substrate having thereon a patterned small molecule organicsemiconductor layer, and the patterned substrate itself, wherein thepatterned small molecule organic semiconductor layer is produced fromthe thermal transfer of the small organic molecule from a donor. Thesmall organic molecule feature distinguishes the present invention fromthose that have transferred polymer or polymer semiconductors from onesurface to a second surface in several ways. There is interest in theuse of small molecule organic semiconductors in manufacturing items suchas light emitting diodes, photodiodes, and field effect transistors(FET's). The present invention provides a cost savings from the usualmethod of semiconductor device production which normally employsexpensive lithographic processes here circumvented by the presentinvention.

[0024] Organic semiconductors are generally cheaper to produce for theseapplications and are also easier to process as they can be deposited atlow temperatures. In addition, this widens the choice of possiblesubstrates including flexible ones that are available in large areassuch as MYLAR™ and KAPTON™.

[0025] The prior art does not disclose the transfer of small moleculesusing a simple process of thermal transfer to form patterned layers ofthe small organic molecule semiconductor material in crystalline form ona substrate.

[0026] Accordingly, it is an object of the present invention to providea method and a system for producing a substrate having thereon apatterned small molecule organic semiconductor layer produced byexposing a donor substrate having thereon a small molecule organicsemiconductor layer to energy thus causing the thermal transfer of thesmall organic molecule onto an acceptor substrate to form the patternedsmall molecule organic semiconductor layer thereon. The principalapplication addresses the manufacture of organic field effecttransistors (FET's) and organic light emitting diodes on a large scalethat that is essentially automated. However, the apparatus and methodare not limited to pentacene and can have applications to organiccompounds other than pentacene, especially small organic semiconductormolecules.

SUMMARY OF THE INVENTION

[0027] The present invention provides a substrate having thereon apatterned small molecule organic semiconductor layer having a smallorganic molecule thermally transferred by exposing a donor substratehaving thereon a small molecule organic semiconductor layer to energy.

[0028] The present invention further provides a method of preparing asubstrate having thereon a patterned small molecule organicsemiconductor layer, involving the exposure of a donor substrate havingthereon a small molecule organic semiconductor layer to energy producedfrom an energy source to cause the thermal transfer of a small organicmolecule onto an acceptor substrate to produce a substrate havingthereon the patterned small molecule organic semiconductor layer.

[0029] The present invention also provides a system for producing asubstrate having thereon a patterned small molecule organicsemiconductor layer. The system has a donor substrate having thereon asmall molecule organic semiconductor layer; an acceptor substratepositioned to receive said patterned small molecule organicsemiconductor layer upon exposing the donor substrate to energy; and anenergy source to produce said energy to cause the thermal transfer of asmall organic molecule onto the acceptor substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 shows a substrate having thereon a patterned small moleculeorganic semiconductor layer.

[0031]FIG. 2 shows a system incorporating an acceptor substrate, a donorsubstrate of energy absorbing material having thereon a small moleculeorganic semiconductor layer, and energy produced from an energy sourceyielding a maskless pattern on the acceptor substrate.

[0032]FIG. 3 shows a system incorporating an acceptor substrate, a donorsubstrate of energy transparent material having thereon a small moleculeorganic semiconductor layer with an energy absorbing film interposedbetween the two, and energy produced from an energy source.

[0033]FIG. 4 shows a representative system of this invention with meansfor moving the donor and acceptor substrates relative to each other andthe energy.

[0034]FIG. 5 shows a representative system of this invention with meansfor moving the energy source relative to the acceptor and donorsubstrates.

[0035]FIG. 6(a) shows an acceptor substrate with means for movement andan energy transparent donor substrate with means for movement, a smallmolecule organic semiconductor layer, an energy absorbing film, and asource of energy with means for movement wherein the energy floodilluminates the donor substrate. The energy absorbing film absorbs theenergy thereby heating the small molecule organic semiconductor layer,thus causing the thermal transfer of the small organic molecule which ispatterned onto the acceptor substrate by the insertion of a mask betweenthe donor and acceptor substrates.

[0036]FIG. 6(b) shows a top view of a mask with an “H” pattern openingand an acceptor substrate behind the mask.

[0037]FIG. 7 shows a representative system and method of the inventionwith the donor substrate being a rotatable disk with means to rotatearound its axis and means to move the rotatable disk relative to theenergy source and the acceptor substrate. The energy source and acceptorsubstrate also have means for movement.

[0038]FIG. 8 shows a representative system and method of the inventionwhere the acceptor substrate has a component of an electronic structurethereon.

[0039]FIG. 9 shows an acceptor substrate with the elements of a fieldeffect transistor (FET) thereon and a patterned small molecule organicsemiconductor layer deposited as the channel of the FET without the useof a mask.

[0040]FIG. 10 shows a reel-to-reel apparatus where the donor substrateis a ribbon that is wound from one reel to the other while energy causesthe thermal transfer of small molecule from the donor substrate to theacceptor substrate.

[0041]FIG. 11(a) shows a side view of a hollow cylindrical roller wherethe energy source is at a point along the axis. The hollow cylindricalroller is here constructed of an energy transparent material and hasthereon a small molecule organic semiconductor layer with an energyabsorbing film therebetween. The energy from the energy source isincident on the inner surface of the hollow cylindrical roller in thedirection of the acceptor substrate and causes the thermal transfer ofsmall molecule from the hollow cylindrical roller to the acceptorsubstrate. This figure illustrates the optional means for exertingpressure on the hollow cylindrical roller to place it in intimatecontact with the acceptor substrate.

[0042]FIG. 11(b) shows a cross sectional view of a hollow cylindricalroller where the energy source is at a point along the axis with theability to move along the axis and to have the axis moved relative tothe hollow cylindrical roller.

[0043]FIG. 12 shows an energy transparent donor substrate with an energyabsorbing film and a small molecule organic semiconductor layer passingin intimate contact with an acceptor substrate between a hollowcylindrical roller with an energy source at a point within and a secondroller. Each roller depicted has optional means for exerting pressure.

DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention provides a substrate having thereon apatterned small molecule organic semiconductor layer having a smallorganic molecule thermally transferred by exposing a donor substratehaving thereon a small molecule organic semiconductor layer to energy.

[0045] The present invention further provides a method of preparing asubstrate having thereon a patterned small molecule organicsemiconductor layer, involving the exposure of a donor substrate havingthereon a small molecule organic semiconductor layer to energy producedfrom an energy source to cause the thermal transfer of a small organicmolecule onto an acceptor substrate to produce a substrate havingthereon the patterned small molecule organic semiconductor layer.

[0046] The present invention also provides system for producing asubstrate having thereon a patterned small molecule organicsemiconductor layer. The system has a donor substrate having thereon asmall molecule organic semiconductor layer; an acceptor substratepositioned to receive said patterned small molecule organicsemiconductor layer upon exposing the donor substrate to energy; and anenergy source to produce said energy to cause the thermal transfer of asmall organic molecule onto the acceptor substrate.

[0047] The present invention provides a substrate having thereon apatterned small molecule organic semiconductor layer. FIG. 1 shows across sectional view of a substrate 100 with a patterned small moleculeorganic semiconductor layer 105. The substrate with the patterned smallmolecule organic semiconductor layer is prepared by exposing a donorsubstrate which has a small molecule organic semiconductor layer on itto energy produced from an energy source. The exposure causes thermaltransfer, such as sublimation and deposition, of a small organicmolecule from the small molecule organic semiconductor layer on thedonor substrate and the deposition of that small molecule onto anacceptor substrate

[0048] The donor substrate can be made of an energy absorbing or anenergy transparent material, or a combination of absorbing andtransparent materials. The donor substrate may also contain areas notdirectly involved with the thermal transfer process that are neithertransparent nor absorptive to energy.

[0049] When the donor substrate is made of an energy absorbing material,the small molecule organic semiconductor layer is directly on the donorsubstrate. In this case the energy is absorbed by the energy absorbingmaterial and heat is produced. It is this heat that causes the thermaltransfer of the small organic molecule onto the acceptor substrate.

[0050]FIG. 2 shows a cross sectional view of a simple system of thepresent invention and is illustrative of the method involving an energyabsorbing donor substrate. A small molecule organic semiconductor layer200 has been pre-deposited on an energy absorbing donor substrate 205.The small molecule organic semiconductor layer 200 can also be producedby the at least partial conversion of a precursor of the small organicmolecule during the step of exposing the donor substrate to energy. Thispreferred embodiment of preparing the small molecule organicsemiconductor layer from a precursor is discussed in further detailbelow and can be employed in all embodiments of the current invention.In FIG. 2 energy 215 from energy source 210 is incident on the surfaceof the energy absorbing donor substrate 205 opposite the small moleculeorganic semiconductor layer 200. This is a preferred direction fromwhich to direct the energy, however, a person of ordinary skill in theart would be capable of configuring the direction in a variety of ways.Energy 215 is absorbed by the energy absorbing donor substrate 205. Heatfrom the absorption of energy 215 is rapidly transferred to the smallmolecule organic semiconductor layer 200 causing the thermal transfer ofthe small organic molecule from the surface of the donor substrate 205to the acceptor substrate 100 depositing a patterned small moleculeorganic semiconductor layer 225 corresponding in area to the heatedregion of the small molecule organic semiconductor layer 200 on thedonor substrate 205. Depending on the relative positioning of the energy215, donor substrate 205, and the acceptor substrate 100 a wide varietyof patterns of the small organic molecule can be formed on the acceptorsubstrate 100. FIG. 2 shows a single region of deposition indicated bythe patterned small molecule organic semiconductor layer 225 whichcorresponds to the diameter of the energy 215.

[0051] When the donor substrate is made of an energy transparentmaterial, an energy absorbing film, such as a thin film, can beinterposed between the donor substrate and the small molecule organicsemiconductor layer. In this case the energy passes through the energytransparent material of the donor substrate and is absorbed by theenergy absorbing film, thus producing heat. It is this heat that causesthe thermal transfer of the small organic molecule onto the acceptorsubstrate. Non-limiting examples of materials for the energy absorbingfilm include platinum, titanium, chromium, and organics such as KAPTON™.

[0052]FIG. 3 shows a cross sectional view of another simple system ofthe present invention and is illustrative of the method involving anenergy transparent donor substrate. A small molecule organicsemiconductor layer 200 has been pre-deposited on an energy transparentdonor substrate 300 with an energy absorbing film 305 interposed between200 and 300. Energy 215 from energy source 210 is incident on thesurface of the energy transparent donor substrate 300 opposite the smallmolecule organic semiconductor layer 200. Energy 215 penetrates theenergy transparent substrate 300 and is absorbed by the energy absorbingfilm 305. Heat from the absorption of energy 215 is rapidly transferredto the small molecule organic semiconductor layer 200 causing thethermal transfer of the small organic molecule from the surface of thedonor substrate 300 to the acceptor substrate 100 depositing a patternedsmall molecule organic semiconductor layer 225 corresponding in area tothe heated region of the small molecule organic semiconductor layer 200on the donor substrate 300. Depending on the relative positioning of theenergy 215, donor substrate 300, and the acceptor substrate 100 a widevariety of patterns of the small organic molecule can be formed on theacceptor substrate 100. FIG. 3 shows a single region of depositionindicated by the patterned small molecule organic semiconductor layer225 which corresponds to the diameter of the energy 215.

[0053] The donor substrate can be made of any suitable material.Non-limiting examples of materials that are suitable for use as thedonor substrate include glass, silicon, polyimide, and polymethylmethacrylate (PMMA).

[0054] The acceptor substrate can be made of any suitable material.Non-limiting examples of materials that are suitable for use as theacceptor substrate include glass, silicon, polyimide, and polymethylmethacrylate (PMMA).

[0055] The energy absorbing film can be of a thickness of from about 100to about 20,000 Angstroms. The energy absorbing film can be applied tothe donor substrate by any well known process. Non-limiting examples ofapplication methods include sputtering, evaporating, spraying, dipping,spinning, or combinations thereof.

[0056] The small molecule organic semiconductor layer can also beapplied to the donor substrate by any well known process. Non-limitingexamples of application methods include sputtering, evaporating,spraying, dipping, spinning, or combinations thereof.

[0057] As mentioned previously, the small molecule organic semiconductorlayer on the donor substrate can be a film, such as a thin film, of thesmall organic molecule itself or it can be formed during the step ofexposing the donor substrate to energy from a precursor of the smallorganic molecule.

[0058] In the context of the present invention, the term small organicmolecule refers to a non-polymeric organic semiconducting material whichis a solid. Examples of such small organic molecules include polycyclicaromatic compounds, such as oligothiophene, perylene,benzo[ghi]perylene, coronene and polyacene.

[0059] In the case that the small molecule organic semiconductor layeris formed from a precursor, the chemical structure of the precursor issuch that only the small organic molecule becomes transferred by thermaltransfer upon application of energy. The remaining chemical constituentsof the precursor become volatized and do not deposit on the acceptorsubstrate.

[0060] The small molecule organic semiconductor layer can be made up ofthe small organic molecule that is to be thermally transferred to theacceptor substrate. The small organic molecule can be a polycyclicaromatic compound. Non-limiting examples of polycyclic aromaticcompounds that are useful in the present invention includeoligothiophene, perylene, benzo[ghi]perylene, coronene, and polyacene.Preferred polyacenes include those represented by the formula:

[0061] wherein each R³, R⁴, R⁵ and R⁶ is independently selected from thegroup consisting of: hydrogen, alkyl of 1-12 carbon atoms, aryl,substituted aryl, a group wherein R³ and R⁴ together form one or morefused benzo rings and a group wherein R⁵ and R⁶ together form one ormore fused benzo rings; wherein n is at least 1. Pentacene, which is anexample of a polyacene, is a preferred, but non-limiting, example of thesmall organic molecules that can be utilized in this invention.

[0062] When the small molecule organic semiconductor layer is producedfrom a precursor of the small organic molecule, the precursor can be,for example, a precursor to a polycyclic aromatic compound; Diels-Alderadduct of a polycyclic aromatic compound with a dienophile, wherein thepolycyclic aromatic compound is selected from: oligothiophene, perylene,benzo[ghi]perylene, coronene and polyacene; and wherein the dienophileis represented by the formula:

R¹—X═Y—R²

[0063] wherein each X and Y can independently be N or CR⁷; wherein R¹—X═can be O, S, SO and SO₂; and

[0064] wherein each R¹, R² and R⁷ can independently be hydrogen, alkylof 1-12 carbon atoms, aryl, substituted aryl, aralkyl, alkoxycarbonyl,aryloxycarbonyl, acyl and a group R, wherein R can be hydrogen, alkyl of1-12 carbon atoms, alkoxy, acyl, aryl, aralkyl, chloroalkyl, fluoroalkyland substituted aryl having a substituent selected from: —F, —Cl, —Br,—NO₂, —CO₂R, —PO₃H, —SO₃H, trialkylsilyl and acyl; wherein the acyl isrepresented by the formula: R⁸CO— wherein R⁸ can be hydrogen, alkyl of1-12 carbon atoms, aryl, substituted aryl, aralkyl and fluoroalkyl;

[0065] with the proviso that at least one of X and Y is a hetero atomselected from: N, O and S.

[0066] A preferred Diels-Alder adduct of a polycyclic aromatic compoundwith a dienophile is represented by the formula:

[0067] wherein each X and Y is independently selected from: N and CR⁷;

[0068] wherein R¹—X═ can be O, S, SO and SO₂; and

[0069] wherein each R¹, R² and R⁷ is independently selected from:hydrogen, alkyl of 1-12 carbon atoms, aryl, substituted aryl, aralkyl,alkoxycarbonyl, aryloxycarbonyl, acyl and a group R, wherein R can behydrogen, alkyl of 1-12 carbon atoms, alkoxy, acyl, aryl, aralkyl,chloroalkyl, fluoroalkyl and substituted aryl having a substituentselected from: —F, —Cl, —Br, —NO₂, —CO₂R, —PO₃H, —SO₃H, trialkylsilyland acyl; wherein the acyl is represented by the formula: R⁸CO— whereinR⁸ can be hydrogen, alkyl of 1-12 carbon atoms, aryl, substituted aryl,aralkyl and fluoroalkyl;

[0070] with the proviso that at least one of X and Y is a hetero atomselected from: N, O and S

[0071] The Diels-Alder adduct of a polycyclic aromatic compound with adienophile can be prepared by a process comprising the step ofcontacting:

[0072] (a) a polycyclic aromatic compound selected from: oligothiophene,perylene, benzo[ghi]perylene, coronene and a compound represented by theformula:

[0073]  wherein each R³, R⁴, R⁵ and R⁶ is independently selected from:hydrogen, alkyl of 1-12 carbon atoms, aryl, substituted aryl, a groupwherein R³ and R⁴ together form one or more fused benzo rings and agroup wherein R⁵ and R⁶ together form one or more fused benzo rings,wherein n is at least 1; and

[0074] (b) dienophile represented by the formula:

R¹—X═Y—R²

[0075]  wherein each X and Y is independently selected from: N and CR⁷;wherein R¹—X═ can be O, S, SO and SO₂; wherein each R¹, R² and R⁷ isindependently selected from: hydrogen, alkyl of 1-12 carbon atoms, aryl,substituted aryl, aralkyl, alkoxycarbonyl, aryloxycarbonyl, acyl and agroup R, wherein R can be hydrogen, alkyl of 1-12 carbon atoms, alkoxy,acyl, aryl, aralkyl, chloroalkyl, fluoroalkyl and substituted arylhaving a substituent selected from: —F, —Cl, —Br, —NO₂, —CO₂R, —PO₃H,—SO₃H, trialkylsilyl and acyl; wherein the acyl is represented by theformula: R⁸CO— wherein R⁸ can be hydrogen, alkyl of 1-12 carbon atoms,aryl, substituted aryl, aralkyl and fluoroalkyl; with the proviso thatat least one of X and Y is a hetero atom selected from: N, O and S;

[0076] wherein the contacting is carried out under reaction conditionssufficient to produce the Diels-Alder adduct.

[0077] A film, such as a thin film, of a Diels-Alder adduct of apolycyclic aromatic compound with a dienophile can be prepared by amethod comprising the steps of:

[0078] (a) applying onto a substrate a solution of a Diels-Alder adductof a polycyclic aromatic compound with a dienophile in a suitablesolvent, wherein the polycyclic aromatic compound is selected from:oligothiophene, perylene, benzo[ghi]perylene, coronene and a compoundrepresented by the formula:

[0079]  wherein each R³, R⁴, R⁵ and R⁶ is independently selected from:hydrogen, alkyl of 1-12 carbon atoms, aryl, substituted aryl, a groupwherein R³ and R⁴ together form one or more fused benzo rings and agroup wherein R⁵ and R⁶ together form one or more fused benzo rings,wherein n is at least 1; and

[0080]  wherein the dienophile is represented by the formula:

R¹—X═Y—R²

[0081]  wherein each X and Y is independently selected from: N and CR⁷;wherein R¹—X═ can be O, S, SO and SO₂; and wherein each R¹, R² and R⁷ isindependently selected from: hydrogen, alkyl of 1-12 carbon atoms, aryl,substituted aryl, aralkyl, alkoxycarbonyl, aryloxycarbonyl, acyl and agroup R, wherein R can be hydrogen, alkyl of 1-12 carbon atoms, alkoxy,acyl, aryl, aralkyl, chloroalkyl, fluoroalkyl and substituted arylhaving a substituent selected from: —F, —Cl, —Br, —NO₂, —CO₂R, —PO₃H,—SO₃H, trialkylsilyl and acyl; wherein the acyl is represented by theformula: R⁸CO— wherein R⁸ can be hydrogen, alkyl of 1-12 carbon atoms,aryl, substituted aryl, aralkyl and fluoroalkyl; with the proviso thatat least one of X and Y is a hetero atom selected from: N, O and S; and

[0082] (b) evaporating the solvent to produce the film of theDiels-Alder adduct of the polycyclic aromatic compound with thedienophile.

[0083] A film, such as a thin film, of a polycyclic aromatic compoundcan be prepared by a method comprising the steps of:

[0084] (a) applying onto a substrate a solution of a Diels-Alder adductof a polycyclic aromatic compound with a dienophile in a suitablesolvent, wherein the polycyclic aromatic compound is selected from:oligothiophene, perylene, benzo[ghi]perylene, coronene and a compoundrepresented by the formula:

[0085]  wherein each R³, R⁴, R⁵ and R⁶ is independently selected from:hydrogen, alkyl of 1-12 carbon atoms, aryl, substituted aryl, a groupwherein R³ and R⁴ together form one or more fused benzo rings and agroup wherein R⁵ and R⁶ together form one or more fused benzo rings,wherein n is at least 1; and wherein the dienophile is represented bythe formula:

R¹—X═Y—R²

[0086]  wherein each X and Y is independently selected from: N and CR⁷;wherein R¹—X═ can be O, S, SO and SO₂; and wherein each R¹, R² and R⁷ isindependently selected from: hydrogen, alkyl of 1-12 carbon atoms, aryl,substituted aryl, aralkyl, alkoxycarbonyl, aryloxycarbonyl, acyl and agroup R, wherein R can be hydrogen, alkyl of 1-12 carbon atoms, alkoxy,acyl, aryl, aralkyl, chloroalkyl, fluoroalkyl and substituted arylhaving a substituent selected from: —F, —Cl, —Br, —NO₂, —CO₂R, —PO₃H,—SO₃H, trialkylsilyl and acyl; wherein the acyl is represented by theformula: R⁸CO— wherein R⁸ can be hydrogen, alkyl of 1-12 carbon atoms,aryl, substituted aryl, aralkyl and fluoroalkyl; with the proviso thatat least one of X and Y is a hetero atom selected from: N, O and S;

[0087] (b) evaporating the solvent to produce the film of theDiels-Alder adduct of the polycyclic aromatic compound with thedienophile; and

[0088] (c) heating the film of the Diels-Alder adduct at a temperatureand for a period of time sufficient to convert the Diels-Alder adductback to the polycyclic aromatic compound.

[0089] Other fused aromatic compounds like oligothiophene, perylene(III), benzo[ghi]perylene (IV), coronene (V) and other fused aromaticcompounds capable of forming Diels-Alder adducts can also be used toprepare soluble precursors of these sparingly soluble compounds.

[0090] wherein n is equal or greater than 1, and preferably from 1 to 5;and wherein R¹ and R² are independently selected from the groupconsisting of hydrogen, alkyl of 1-12 carbon atoms, acyl,alkylphosphonate, hydroxyalkyl, mercaptoalkyl, thiol, carboxylic acid,carboxylic acid ester, trialkoxysilane, amino, alkylamino, dialkylaminoand aminoalkane.

[0091] A most preferred polycyclic aromatic compound is pentacene.Pentacene, a small molecule organic semiconductor is particularly usefulin making organic field effect transistors (FET's), as well as organiclight emitting diodes. Such organic semiconductors are particularlyattractive as they require relatively low temperature processing, thematerials are relatively inexpensive and they can be deposited onflexible substrates. These qualities are all advantageous compared toconventional silicon technology as it is employed today in manufacturingof these devices.

[0092] An example of such an adduct wherein the polycyclic aromaticcompound is pentacene and the dienophile is a thioxocarboxylate isrepresented by the formula:

[0093] The above Diels-Alder adduct in which the sulfur atom is oxidizedto the corresponding sulfoxide is represented by the formula:

[0094] wherein R is selected from: hydrogen, alkyl of 1-12 carbon atoms,alkoxy, acyl, aryl, aralkyl, chloroalkyl, fluoroalkyl and substitutedaryl having a substituent selected from: —F, —Cl, —Br, —NO₂, —CO₂R,—PO₃H, —SO₃H, trialkylsilyl and acyl; wherein said acyl is representedby the formula: R⁸ CO— wherein R⁸ is selected from: hydrogen, alkyl of1-12 carbon atoms, aryl, substituted aryl, aralkyl and fluoroalkyl;

[0095] Another example is the Diels-Alder reaction of thioxomalonatewith pentacene to form an adduct with one carbon-sulfur bond as depictedin the following scheme. Diethyl thioxomalonate is prepared in situ fromthe reaction of diethyl oxomalonate and phosphorous pentasulfide andreacted with pentacene in the presence of a catalyst or by heating inpyridine.

[0096] wherein each R is independently selected from: hydrogen, alkyl of1-12 carbon atoms, alkoxy, acyl, aryl, aralkyl, chloroalkyl, fluoroalkyland substituted aryl having a substituent selected from: —F, —Cl, —Br,—NO₂, —CO₂R, —PO₃H, —SO₃H, trialkylsilyl and acyl; wherein said acyl isrepresented by the formula: R⁸CO— wherein R⁸ is selected from: hydrogen,alkyl of 1-12 carbon atoms, aryl, substituted aryl, aralkyl andfluoroalkyl;

[0097] At temperatures higher than 150° C., the thioxomalonate adduct,which is isolated by column chromatography as a white crystallinecompound, undergoes a retro Diels-Alder reaction to pentacene. However,if the sulfide is oxidized to corresponding S-oxide, then the adduct canbe converted back to pentacene at temperature as low as 150° C.

[0098] Both the sulfide and S-oxide adduct are highly soluble in commonorganic solvents and can be processed from solution to form films onsubstrates.

[0099] Another class of adducts of pentacene is Diels-Alder reactionproducts of pentacene and dialkyl or diaralkylazodicarboxylates. Thesecompounds are by themselves thermally labile and decompose above 100° C.Therefore, any Diels-Alder reaction of these compounds with pentacenehas to be carried out low to moderate temperature.

[0100] The Diels-Alder adduct where the dienophile is anazodicarboxylate of the formula RO—CO—N═N—COOR is shown below:

[0101] R can be alkyl of 1-12 carbon atoms, aryl, aralkyl, chloroalkyl,fluoroalkyl and substituted aryl having a substituent selected from: —F,—Cl, —Br, —NO₂, —CO₂R, trialkylsilyl and acyl; wherein the acyl isrepresented by the formula: R⁸CO— wherein R⁸ can be hydrogen, alkyl of1-12 carbon atoms, aryl, substituted aryl, aralkyl, chloroalkyl andfluoroalkyl.

[0102] Preferably, R is benzyl, alkyl of one to five carbon atoms,partially or fully chlorinated alkyl of one to four carbon atoms andpartially or fully fluorinated alkyl of one to four carbon atoms.

[0103] The above Diels-Alder can be hydrolyzed to form a cyclic diaminecompound represented by the formula:

[0104] and the diamine can be oxidized to give an azo compoundrepresented by the formula:

[0105] Employing a Lewis acid catalyst, such as, titanium tetrachloridefacilitates the Diels Alder reaction so it can be carried out attemperature below −40° C. Alternatively, less active catalysts likesilver tetrafluoroborate or methyl rhenium trioxide can be used to runthe reaction above room temperature by refluxing the mixture ofpentacene, diazodicarboxylate and the catalyst in a low boiling solventlike THF or chloroform.

[0106] These diaza adducts of pentacene are stable to high temperaturesand as such are not good candidates as pentacene precursors becausefilms of these compounds have to be heated above 280° C. to convert topentacene. For example, the adduct of diethyl diazodicarboxylate(R=ethyl) has a melting point of 257° C. and is stable up to 300° C. Butwhen the carboxylate groups are hydrolyzed to the corresponding acid,which automatically undergo decarboxylation to form the cyclic diamine,or oxidized form of the latter to diazo derivative, then the adductbecomes highly unstable and can be converted back to pentacene atmoderate temperatures (50-100° C.). Thus, an important step in thisprocess is the removal of the carboxylate protecting group at lowtemperatures so as to be able to isolate the amine or diazo compounds.

[0107] The adducts of pentacene with a variety of dialkylazodicarboxylate were prepared. It was found that bis-trichloroethylcarboxylates (R═CCl₃—CH₂—) can easily be removed at room temperature inTHF by treatment with zinc powder to give the corresponding diamine.

[0108] In yet another example of Diels-Alder reaction of pentacene withhetero dienophiles, N-Sulfinyl acetamide (R═CH₃CO—) and N-sulfinylbenzyl carbamate (R═C₆H₅CH₂OCO—) were prepared and reacted withpentacene in the presence of methyl rhenium trioxide as Lewis acidcatalyst. In both cases, high yields of the adduct were obtained and thecompounds found to be highly soluble in many organic solvents.

[0109] Films of these compounds were cast from solution and then heatedat 120-140° C. to transform the compounds back to pentacene is confirmedby its UV/VIS spectra and thermogravimetric analysis TGA and IRspectrum. Although the onset of the retro Diels-Alder reactiontemperature for bulk, as evident from TGA, is about 140° C., films ofthese compounds can be converted back to pentacene at even lowertemperatures of 110-120° C.

[0110] In still another example of Diels-Alder reaction of pentacenewith hetero dienophiles, a Diels-Alder adduct wherein the dienophile isan N-sulfinyl amide compound is represented by the formula:

RCO—N═S═O

[0111] and the adduct is represented by the formula:

[0112]  wherein R can be hydrogen, alkyl of 1-12 carbon atoms, alkoxy,acyl, aryl, aralkyl, chloroalkyl, fluoroalkyl and substituted arylhaving a substituent selected from: —F, —Cl, —Br, —NO₂, —CO₂R, —PO₃H,—SO₃H, trialkylsilyl and acyl; wherein the acyl is represented by theformula: R⁸CO— wherein R⁸ can be hydrogen, alkyl of 1-12 carbon atoms,aryl, substituted aryl, aralkyl and fluoroalkyl.

[0113] The above Diels-Alder adduct can be hydrolyzed to form a compoundrepresented by the formula:

[0114] Although only two examples of N-sulfinyl amides are shown here,N-sulfinyl derivatives are equally attractive candidates for thepreparation of soluble pentacene adducts.

[0115] For example, N-sulfinyl derivative of fluoroalkylamide liketrifluoracetamide (R═CF₃—CO—) or higher alkyl amides(R═C_(n)H_(2n+1)—CO—, where n=1-10) can be used instead of sulfinylacetamide. N-Sulfinyl derivatives of aromatic amines (R=aryl) where R—is simply a phenyl group or substituted (nitro, keto, halo, alkyl,fluoroalkyl etc) are known to undergo Diels-Alder reactions and can beused to prepare soluble adducts with pentacene.

[0116] In another example of the Diels-Alder reaction of pentacene witha hetero dienophile, a Diels-Alder adduct wherein the dienophile is anitroso compound is represented by the formula:

[0117] wherein R can be hydrogen, alkyl of 1-12 carbon atoms, alkoxy,acyl, aryl, aralkyl, chloroalkyl, fluoroalkyl, substituted aryl having asubstituent selected from: —F, —Cl, —Br, —NO₂, —CO₂R, —PO₃H, —SO₃H,trialkylsilyl and acyl; wherein the acyl is represented by the formula:R⁸CO— wherein R⁸ can be hydrogen, alkyl of 1-12 carbon atoms, aryl,substituted aryl, aralkyl and fluoroalkyl.

[0118] Other acylnitroso compounds of general formula R—CO—N═O are veryattractive and judged by its adduct with anthracene derivative can beconverted back to pentacene at moderate temperatures. An example wouldbe the reaction of pentacene with N-oxyacetamide (R═CH₃—) which can begenerated from acetylhydroxamic acid and reacted with pentacene in thepresence of methyl rhenium trioxide to give desired adduct as shownbellow.

[0119] In the above reaction R— can be chosen from alkyl groups ofhaving one to twelve carbon atoms, halogenated alkyl groups likeCF₃—(CF₂)_(n)— where n is from zero to 10. R could be also an aryl grouplike phenyl or substituted phenyl with substituents like one or morehalogens (Cl, F and Br), nitro group, carboxylic acid or esters, aminesor amides, phosphonic acid or ester, trialkyl or trialkoxysilane.

[0120] The adducts in which nitrogen is connected to an acyl (RCO) groupcould further be hydrolyzed to corresponding —NH group by treatment withbase as shown in the following reaction.

[0121] Films of these adducts are prepared from solution by differenttechniques, e.g., spin-coating, casting, doctor blading, etc. Once filmsof these adducts on substrates are formed, they can easily be convertedback to pentacene by heating the substrate on a hot plate or in an ovenat modest temperatures. Any residual compounds other than pentaceneformed during retro Diels-Alder reaction can be removed by dipping thesubstrate solvents like alcohols, ethers, ketones and the like, to getpure pentacene films.

[0122] In the examples listed above the diene which was employed inDiels-Alder reactions has been pentacene, but other members ofpolyacenes like tetracene, hexacene and heptacene (structure I, n=2, 4and 5 respectively) can also be used to make soluble derivatives withhetero dienophiles.

[0123] Although in all the structures depicted so far, the dienophilehas attached to the middle ring of pentacene (or polyacene in general)it is possible to have the dienophile react with other ring inpolycyclic aromatic compounds like pentacene, as depicted in thefollowing structure with R¹—X═Y—R² representing hetero dienophiles ofthis invention:

[0124] wherein each X and Y is independently selected from: N and CR⁷;

[0125] wherein R¹—X═ can be O, S, SO and SO₂; and

[0126] wherein each R¹, R² and R⁷ is independently selected from:hydrogen, alkyl of 1-12 carbon atoms, aryl, substituted aryl, aralkyl,alkoxycarbonyl, aryloxycarbonyl, acyl and a group R, wherein R can behydrogen, alkyl of 1-12 carbon atoms, alkoxy, acyl, aryl, aralkyl,chloroalkyl, fluoroalkyl and substituted aryl having a substituentselected from: —F, —Cl, —Br, —NO₂, —CO₂R, —PO₃H, —SO₃H, trialkylsilyland acyl; wherein the acyl is represented by the formula: R⁸CO— whereinR⁸ can be hydrogen, alkyl of 1-12 carbon atoms, aryl, substituted aryl,aralkyl and fluoroalkyl;

[0127] with the proviso that at least one of X and Y is a hetero atomselected from: N, O and S.

[0128] In the cases where the small molecule organic semiconductor layeris produced by at least a partial conversion of a precursor of the smallorganic molecule during the step of exposing the donor substrate toenergy the donor substrate has a predeposited thin precursor filmthereon. When the donor substrate, and optionally the energy absorbingfilm, are exposed to the energy, the resultant heat causes theconversion of the precursor to the small molecule organic semiconductorlayer and the thermal transfer of the small organic molecule onto theacceptor substrate.

[0129] In certain situations, some precursor will sublime and depositonto the acceptor substrate without conversion to the small organicmolecule. In these situations the acceptor substrate can be annealedafter the thermal transfer at about the thermal decompositiontemperature of the precursor to convert any remaining precursor to thesmall organic molecule.

[0130] It has also been shown that heating the acceptor substrate priorto thermal transfer improves the thermal transfer of the small organicmolecule onto the acceptor substrate. Heating is carried out at atemperature in the range from about 25° C. to about 100° C., preferablyfrom about 25° C. to about 75° C., depending on the particular smallmolecule. This heating can be used alone or in combination with theannealing discussed above.

[0131] The energy used to expose the donor substrate can be selectedfrom any sufficient to cause the thermal transfer of the small organicmolecule and the conversion of any precursor used. Non-limiting examplesof suitable energy from an energy source are infrared, ultraviolet,visible, thermal, electron beam, ion beam, x-ray beam, energy beam,pulsed energy, continuous wave (cw) energy, focused laser, pulsed laser,cw laser, thermal probe, resistive heating, a heated AFM probe, asoldering iron tip, or any combination thereof. A non-limiting exampleof resistive heating includes resistance losses due to the passage of alocal current pulse in contact with the donor substrate. The energysource can produce energy that exposes small portions of the donorsubstrate at a time to the energy. The energy source can optionallyproduce energy that floods the donor substrate with energy. A mostpreferred energy is a focused laser beam.

[0132] In the current invention the donor substrate may be movedrelative to the energy source and the acceptor substrate. Also, theenergy may be moved relative to the donor substrate and the acceptorsubstrate. Non-limiting examples of this movement include moving theenergy source itself and scanning the energy relative to the substrates.Furthermore, the acceptor substrate may be moved relative to the energysource and the donor substrate. All of these movements can be employedsingly or in combination. Means for and methods of implementing thesemovements are well known and one of ordinary skill in the art should becapable of configuring.

[0133]FIG. 4 shows a simple system of the present invention having meansfor moving the acceptor substrate 400 and means for moving the donorsubstrate 405 relative to each other and the energy 215 from energysource 210. FIG. 4 shows an energy absorbing donor substrate system withan energy absorbing substrate 205 and small molecule organicsemiconductor layer 200 for example purposes only, and is not meant tolimit the application of the means of movement.

[0134]FIG. 5 shows a simple system of the present invention having meansfor moving the energy source 500 relative to the donor substrate 300(here, a transparent substrate by example) and acceptor substrate 100.By employing any of the means for movement illustrated in FIGS. 4 and 5,alone or in combination, it is possible to create patterns of the smallorganic molecule on the surface of the acceptor substrate 100 asindicated by the patterned small molecule organic semiconductor layer105 in FIG. 1.

[0135] An alternative embodiment can further include, possiblyeliminating the need to move the substrates and the energy, a maskplaced between the donor substrate and the acceptor substrate. FIG. 6ashows a cross sectional view of a simple system of the present inventionwhere a mask 620 with a solid portion 630 and an open portion 625. Theopen portion 625 corresponds to the desired dimensions of the patternedsmall molecule organic semiconductor layer 105 to be produced on theacceptor substrate 100. Flood energy 615 is incident on the donorsubstrate 300 (here, an energy transparent substrate by example). As thegenerated heat is transferred from the entire illuminated region ofenergy absorbing film 305, the small molecule organic semiconductorlayer 200 sublimes. The solid portion 630 of the mask 625 acts as aphysical block to the subliming and depositing small molecule and allowspatterning on the acceptor substrate 100 of the patterned small moleculeorganic semiconductor layer 105.

[0136]FIG. 6b shows a top view of a mask 620 with solid portion 630 andopen portion 625. Here, the open portion 625 is dimensioned as an “H”pattern, however, any desired pattern dimensions can be utilized. Theacceptor substrate 100 is visible below the mask.

[0137] In another embodiment the donor substrate is a disk mounted on arotatable axis. The donor substrate can be rotated around the axis andthe energy incident at a point on the donor substrate. As the donorsubstrate rotates, the energy causes the heating, and thus the thermaltransfer, of a new portion of the small molecule organic semiconductorlayer. By displacing the axis relative to the energy and/or by movingthe energy relative to the disk, the entire portion of the smallmolecule organic semiconductor layer can be utilized. The acceptorsubstrate may also be moved.

[0138]FIG. 7 shows a cross sectional view of an example of the diskmounted on a rotatable axis embodiment. Here, an energy transparentsubstrate 300 with an energy absorbing film 305 is used by example. Theenergy transparent substrate 300 is in the form of a rotatable disk 700attached at an axis 710 to a means to rotate the disk 705. Energy 215from energy source 210 is incident on the disk such to cause the heatingof the small molecule organic semiconductor layer 200 pre-depositedthereon and the thermal transfer of the small organic molecule onto theacceptor substrate 100. FIG. 7 shows a patterned small molecule organicsemiconductor layer 225 corresponding to the width of the energy 215. Byrotating the disk 700 a different region of the small molecule organicsemiconductor layer 200 would be affected by the energy 215 and thussublimed and deposited on the acceptor substrate 100. Means fordisplacing the disk axis 715 can be utilized to move the disk 700 inrelation to the energy 215 and acceptor substrate 100, for example tobring energy 215 incident upon a different radius of disk 700 and thusutilize the full area of the small molecule organic semiconductor 200.Alternately or in combination with 715, means for moving the energy 500can be utilized. Means for moving the acceptor substrate 400 can also beutilized singly or in combination with the movement of the othercomponents.

[0139] The method and system of the present invention can be practicedin a vacuum or under regular atmospheric conditions. Under regularatmospheric conditions the donor substrate and acceptor substrate can bein contact or separated slightly, typically by less than 1 cm. It hasalso been unexpectedly found that the thermal transfer is improved whenthe small molecule organic semiconductor layer on the donor substrateand the acceptor substrate are in intimate contact. Intimate contactrefers to having a contact area which is substantially free ofatmospheric gases. In certain situations it is necessary to applypressure to achieve this intimate contact. Non-limiting examples ofmethods of applying pressure include a planar pressure device, anilluminated doctor blade, and a waveguide tip.

[0140] The system, method, and product of the present invention achievethermal transfer of small molecule organic semiconductor orsemiconducting film from one surface to a second surface. This type oftransfer makes it possible, for example, to ‘print’ channels onto fieldeffect transistor structures or to deposit regions of small moleculeorganic semiconducting films for organic light emitting diodes.

[0141] To achieve these examples of the present invention, components toan electronic structure can be added to the substrate. FIG. 8 shows anacceptor substrate 100 having thereon a component to an electronicstructure 800 with a patterned small molecule organic semiconductorlayer 225. In a preferred embodiment, the component to an electronicstructure can comprise source, drain, and gate elements of a fieldeffect transistor. In this preferred embodiment, the patterned smallmolecule organic semiconductor layer forms a channel of the field effecttransistor. FIG. 9 shows one simple example of a field effect transistoron an acceptor substrate 100 with gate 905, gate oxide 910, drain 915,and source 920 elements. The patterned small molecule organicsemiconductor layer 105 forms the channel of the field effecttransistor. In another preferred embodiment, the patterned smallmolecule organic semiconductor layer forms an active layer of an organiclight emitting diode. In another preferred embodiment, the components toan electronic structure are components of a photodiode.

[0142] In yet another embodiment, the donor substrate is a ribbon. Theribbon can be rigid or flexible depending on the application. When thedonor substrate is a ribbon, it is possible for the ribbon to be part ofa reel-to-reel apparatus. FIG. 10 shows a ribbon 1000 (here for examplepurposes only made of a flexible, energy transparent material) with anenergy absorbing film 305 and small molecule organic semiconductor layer200 deposited along the entire length of the ribbon 1000. A preferredreel-to-reel apparatus has a reel 1010 around which is wound the ribbonand another reel 1015 onto which the ribbon is wound as the ribbonpasses through an area where it is exposed to the energy 215 from energysource 210 and the small molecule organic semiconductor layer 200sublimes and is deposited onto the acceptor substrate 100. As the ribbon1000 is wound around spindle 1020 of reel 1015 by a means configurableby one of ordinary skill in the art, a patterned small molecule organicsemiconductor layer 225 (here, for example purposes, dimensionedcorresponding to the radius of the incident energy 215). As with otherembodiments of the invention, it is possible to have means for movingthe energy 500 and means for moving the acceptor substrate 200. Oneresult of this relative movement is the production any number ofdifferent patterns of the small organic molecule on the acceptorsubstrate.

[0143] In still yet another embodiment, the donor substrate is in theshape of a hollow cylindrical roller having an inner and an outersurface. The outer surface is where the small molecule organicsemiconductor layer resides. As is possible in all embodiments of theinvention, when the hollow cylindrical roller is made of an energytransparent material, there can be an energy absorbing film between theouter surface of the hollow cylindrical roller and the small moleculeorganic semiconductor layer. The basic structure of the novel apparatusconsists of a hollow cylinder or drum free to rotate by computercontrol, with the cylinder preferably made from a material thattransmits light in the visible, for example glass or plastic. In oneembodiment, the outer periphery of the cylinder has a thin coating of anoptically absorbing material with the small molecule organicsemiconductor layer disposed thereon. Again, the small organic moleculemay be pentacene or one of its precursors but again not limited to thatparticular small molecule organic semiconductor.

[0144] The energy source can be at a point within the hollow cylindricalroller. The energy source within the hollow cylindrical roller can beone or more laser diodes. Typically, the point is along the axis of thehollow cylindrical roller such that the energy from the energy source isdirected at the inner surface of the hollow cylindrical roller in thedirection of the acceptor substrate. Alternatively, the energy sourcecan be along a line, preferably parallel to the axis of the cylinder.This line can be close to the periphery of the cylinder. A means formoving the axis of the cylinder from the true axis of the cylinder canalso be employed to bring the energy source to different positionsrelative to the periphery of the cylinder. It is possible for thisenergy source to be moveable from one point to another within the hollowcylindrical roller, usually, but not restricted to, along the axis. Theenergy source can be computer controlled with respect to its on-offmodes of operation and location. Typically the on-off modes of operationare controlled with respect to time and the relative position of thehollow cylindrical roller and the energy source. An example of theplacement of the energy source is a single laser diode that can be movedalong the mounting axis and the roller moved stepwise after the laserhas traversed the entire length of the roller axis with the laser pulsedat designated positions to bring about thermal transfer.

[0145] The roller can be rolled in relation to the acceptor substrate. Anon-limiting example of a suitable acceptor substrate is a flat sheet,preferably a plastic sheet placed on a hard, non-compliant surfacewherein the hollow cylindrical roller is made to roll over the plasticsheet and the energy causes the thermal transfer of the small organicmolecule from the outside of the hollow cylindrical roller to theacceptor substrate. As mentioned above, the thermal transfer is improvedwhen the small molecule organic semiconductor layer and the acceptorsubstrate are in intimate contact. Often this intimate contact isachieved through the application of pressure so that the small moleculeorganic semiconductor layer and the acceptor substrate have a contactarea which is substantially free of atmospheric gases. A thermaltransfer of the organic material is made from the cylinder (donor) ontothe acceptor substrate as has been previously shown in a simplerembodiment by experimentation.

[0146] The energy absorbing film and the small molecule organicsemiconductor layer can be applied to the hollow cylindrical roller byany well known method. Examples of these methods include sputtering,evaporating, spraying, dipping, spinning, and combinations thereof.

[0147]FIG. 11a shows a cross sectional view of an example of the hollowcylindrical roller embodiment. Here, hollow cylindrical roller 1100 hasan outer material that is energy transparent with an inner surface 1105and an outer surface 1110. An energy absorbing film 305 has beendisposed on the outer surface 1110 and a small molecule organicsemiconductor layer 200 has been disposed thereon. Energy 215 fromenergy source 210 situated at a point 1120 within the hollow cylindricalroller is incident on the inner surface 1105 in the direction of theacceptor substrate 100 which is to receive the thermal transfer of thesmall organic molecule. FIG. 11a further shows the optional means forapplying pressure 1115. FIG. 11b shows a cut away view of a hollowcylindrical roller 1100 with the energy source 210 positioned at a pointalong the axis 1120 of the hollow cylindrical roller. Means fordisplacing 1125 the axis from true center is shown and the energy source210 is movable along the axis 1120. Energy 215 is incident on the innersurface 1105 of the hollow cylindrical roller. It is possible for thehollow cylindrical roller to be made of an energy absorbing material(not shown) and to have the small molecule organic semiconductor layerdirectly thereon.

[0148] In another embodiment, the energy source is disposed at a pointwithin a hollow cylindrical roller having an inner and an outer surface.Here, the donor substrate is a first rigid or flexible material sheethaving the small molecule organic semiconductor layer thereon. Theacceptor substrate is a second rigid or flexible material sheet. Thematerial sheets are passed simultaneously between the hollow cylindricalrollers and a second roller which are in contact with one another alongtheir longitudinal axes such to permit the thermal transfer of the smallorganic molecule from the first material sheet to the second materialsheet.

[0149] One or both of the two rollers may be slightly compliant, therebyallowing more than just line contact along the axis of the roller. Thisallows thermal transfer of material over small linear distances in adirection that is perpendicular to the axis of the roller alsocontrolled in part by the shape of the energy. The apparatus can be madeto allow for a constant feed-through of both materials to provide largescale production.

[0150] It is possible that the first material sheet and the smallmolecule organic semiconductor layer have an energy absorbing filminterposed between them. Often when the first material sheet is anenergy transparent material, this energy absorbing film is necessary toabsorb the energy. The material sheets can be made of any suitablematerial. In a preferred embodiment the material sheets are made of aflexible plastic. Non-limiting examples of flexible plastic includeMYLAR™ and KAPTON™.

[0151] It is also possible, however, for the first material sheet to bean energy absorbing material.

[0152] The energy source within the hollow cylindrical roller can be oneor more laser diodes. Typically, the energy source is along the axis ofthe hollow cylindrical roller such that the energy from the energysource is directed at the inner surface of the hollow cylindrical rollerin the direction of the acceptor substrate. It is possible for thisenergy source to be moveable from one point to another within the hollowcylindrical roller, usually, but not restricted to, along the axis. Theenergy source can be computer controlled with respect to its on-offmodes of operation. Typically this the on-off modes of operation arecontrolled with respect to time and the relative position of the hollowcylindrical roller.

[0153] As mentioned above, the thermal transfer is improved when thesmall molecule organic semiconductor layer and the acceptor substrateare in intimate contact. Often this intimate contact is achieved throughthe application of pressure so that the small molecule organicsemiconductor layer and the acceptor substrate have a contact area whichis substantially free of atmospheric gases. For example, the two rollerscan be brought into intimate contact at a predetermined compression setby adjustable springs on at least one of the rollers or by any othermeans capable of producing such intimate contact.

[0154]FIG. 12 shows a cross sectional view of an example of theforegoing embodiment. A first material sheet 825 (here made of a energytransparent material) with an energy absorbing film 305 and a smallmolecule organic semiconductor layer 200 and a second material sheet1230 are simultaneously passed between a hollow cylindrical roller 1200and a second roller 1235. Energy 215 from energy source 210 along theaxis 1220 of the hollow cylindrical roller 1200 is incident on the innersurface 1205 of the hollow cylindrical roller 1200. The energy passesthrough the hollow cylindrical roller and the energy transparent firstmaterial sheet 825 thus being absorbed by the energy absorbing film 305causing heat to be transferred to the small molecule organicsemiconductor layer 200. This heat causes the thermal transfer of smallmolecule to the second material sheet 1230. FIG. 12 shows optional means1215 and 1240 for applying pressure.

[0155] To those skilled in the art, it is clear that many possiblevariations of these configurations are possible.

[0156] In addition to being directed to the method for preparing thesubstrate having the patterned small molecule organic semiconductorlayer thereon, this invention is directed to a substrate with apatterned small molecule organic semiconductor layer comprising a smallorganic molecule thermally transferred by exposing a donor substratehaving thereon a small organic molecule organic semiconductor layer toenergy.

[0157] The invention is still further directed to a system for producinga substrate having thereon the patterned small molecule organicsemiconductor layer. Features of the production of a substrate havingthereon the patterned small molecule organic semiconductor have beendiscussed in detail in relation to the method herein above. The systemincludes a donor substrate with a small molecule organic semiconductorlayer thereon; an acceptor substrate positioned to receive the patternedsmall molecule organic semiconductor layer upon exposing the donorsubstrate to energy; and an energy source to produce the energy to causethe thermal transfer of a small organic molecule onto the acceptorsubstrate.

[0158] The features of the following embodiments of the system, andother embodiments of the system have been described in detail inrelation to the method herein above.

[0159] The system of the present invention can also include an energyabsorbing film interposed between the donor substrate and the smallmolecule organic semiconductor layer to absorb the energy and causethermal transfer of the small organic molecule.

[0160] As discussed above in relation to the method the small moleculeorganic semiconductor layer can be produced by an at least partialconversion of a precursor of the small organic molecule during theexposing of the donor substrate.

[0161] The system can have a heating source to anneal the acceptorsubstrate after the thermal transfer of the patterned small moleculeorganic semiconductor layer on the acceptor substrate. The annealing canbe performed at about the thermal decomposition temperature of theprecursor to convert any remaining precursor to small molecule.

[0162] The system can have means for relatively moving the donorsubstrate, acceptor substrate, energy source, or a combination thereof.

[0163] The system can have a mask, wherein the mask is interposedbetween the donor substrate and the acceptor substrate.

[0164] The system can have a donor substrate that is a rigid or flexibleribbon. The ribbon can be part of a reel to reel apparatus.

[0165] The system can have a donor substrate that is a disk mounted on arotatable axis.

[0166] The system can include components of an electronic structure asdescribed in detail relative to the method of the invention.

[0167] The system can have a donor substrate that is in the shape of ahollow cylindrical roller having an inner and an outer surface, whereinthe outer surface has thereon a small molecule organic semiconductorlayer.

[0168] The system can have an energy source that is disposed at a pointwithin a hollow cylindrical roller having an inner and an outer surface;wherein the donor substrate is an optically transparent first rigid orflexible material sheet having an energy absorbing film interposedbetween the donor substrate and a small molecule semiconductor layer. Anacceptor substrate is a second rigid or flexible material sheet. Thefirst and second material sheets are passed simultaneously between thehollow cylindrical roller and a second roller. The rollers can be incontact with one another along their longitudinal axes to permit thethermal transfer of the small organic molecule from the first materialsheet to the second material sheet.

[0169] The present invention has been described with particularreference to the preferred embodiments. It should be understood that theforegoing descriptions and examples are only illustrative of theinvention. Various alternatives and modifications thereof can be devisedby those skilled in the art without departing from the spirit and scopeof the present invention. Accordingly, the present invention is intendedto embrace all such alternatives, modifications, and variations thatfall within the scope of the appended claims.

What is claimed is:
 1. A method of preparing a substrate having thereona patterned small molecule organic semiconductor layer, said methodcomprising: exposing a donor substrate having thereon a small moleculeorganic semiconductor layer to energy produced from an energy source tocause the thermal transfer of a small organic molecule onto an acceptorsubstrate to produce a substrate having thereon said patterned smallmolecule organic semiconductor layer.
 2. The method of claim 1, whereinsaid donor substrate and said small molecule organic semiconductor layerhave an energy absorbing film interposed therebetween.
 3. The method ofclaim 1, wherein said donor substrate is an energy absorbing material oran energy transparent material.
 4. The method of claim 1, wherein saidsmall molecule organic semiconductor layer is produced by at least apartial conversion of a precursor of said small organic molecule duringthe step of exposing said donor substrate.
 5. The method of claim 1,wherein said patterned small molecule organic semiconductor layercomprises a polycyclic aromatic compound, said polycyclic aromaticcompound represented generally by the formula:

wherein each R³, R⁴, R⁵ and R⁶ is independently selected from the groupconsisting of: hydrogen, alkyl of 1-12 carbon atoms, aryl, substitutedaryl, a group wherein R³ and R⁴ together form one or more fused benzorings and a group wherein R⁵ and R⁶ together form one or more fusedbenzo rings; and wherein n is at least
 1. 6. The method of claim 5,wherein said polycyclic aromatic compound is pentacene.
 7. The method ofclaim 4, wherein said precursor is a precursor to a polycyclic aromaticcompound; wherein said precursor to a polycyclic aromatic compound is aDiels-Alder adduct of a polycyclic aromatic compound with a dienophile,wherein said polycyclic aromatic compound is selected from the groupconsisting of: oligothiophene, perylene, benzo[ghi]perylene, coroneneand polyacene; and wherein said dienophile is represented by theformula: R¹—X═Y—R²  wherein each X and Y is independently selected fromthe group consisting of: N and CR⁷;  wherein R¹—X═ is selected from thegroup consisting of: O, S, SO and SO₂; and  wherein each R¹, R² and R⁷is independently selected from the group consisting of: hydrogen, alkylof 1-12 carbon atoms, aryl, substituted aryl, aralkyl, alkoxycarbonyl,aryloxycarbonyl, acyl and a group R, wherein R is selected from thegroup consisting of: hydrogen, alkyl of 1-12 carbon atoms, alkoxy, acyl,aryl, aralkyl, chloroalkyl, fluoroalkyl and substituted aryl having asubstituent selected from the group consisting of: —F, —Cl, —Br, —NO₂,—CO₂R, —PO₃H, —SO₃H, trialkylsilyl and acyl; wherein said acyl isrepresented by the formula: R⁸CO— wherein R⁸ is selected from the groupconsisting of: hydrogen, alkyl of 1-12 carbon atoms, aryl, substitutedaryl, aralkyl and fluoroalkyl; with the proviso that at least one of Xand Y is a hetero atom selected from the group consisting of: N, O andS.
 8. The method of claim 1, wherein said energy is selected from thegroup consisting of: infrared, ultraviolet, visible, thermal, electronbeam, ion beam, energy beam, pulsed energy, continuous wave (cw) energy,focused laser, pulsed laser, cw laser, thermal probe, resistive heating,a heated AFM probe, a soldering iron tip, and combinations thereof. 9.The method of claim 1, wherein said acceptor substrate is heated. 10.The method of claim 9, wherein said heating is carried out in a mannerselected from the group consisting of: (a) prior to said thermaltransfer of said patterned small molecule organic semiconductor layer,wherein said heating is carried out at a temperature in the range fromabout 25° C. to about 100° C., depending on the particular said smallorganic molecule; (b) after said deposition of said patterned smallmolecule organic layer on said acceptor substrate, wherein said heatingis at about the thermal decomposition temperature of said precursor toconvert any remaining precursor to said small organic molecule. (c) anycombination of (a)-(b) above.
 11. The method of claim 1, furthercomprising a step selected from the group consisting of: (a) moving saiddonor substrate relative to said energy source and said acceptorsubstrate; (b) moving said energy relative to said donor substrate andsaid acceptor substrate; (c) moving said acceptor substrate relative tosaid energy source and said donor substrate; and (d) any combination of(a)-(d) above.
 12. The method of claim 1, further comprising: insertinga mask between said donor substrate and said acceptor substrate.
 13. Themethod of claim 1, wherein said donor substrate is a disk mounted on arotatable axis.
 14. The method of claim 1, wherein said energy is afocused laser.
 15. The method of claim 14, wherein said patterned smallmolecule organic semiconductor layer is a channel of a field effecttransistor.
 16. The method of claim 14, wherein said small moleculeorganic semiconductor layer forms an active layer of an organic lightemitting diode.
 17. The method of claim 1, wherein said donor substrateis a rigid or flexible ribbon.
 18. The method of claim 17, wherein saidribbon is part of a reel to reel apparatus.
 19. The method of claim 1,wherein said donor substrate is in the shape of a hollow cylindricalroller having an inner and an outer surface, said outer surface havingthereon said small molecule organic semiconductor layer.
 20. The methodof claim 19, wherein said energy source is at a point within said hollowcylindrical roller.
 21. The method of claim 20, wherein said pointwithin said hollow cylindrical roller is along the axis of said hollowcylindrical roller such that said energy from said energy source isdirected at said inner surface of said hollow cylindrical roller in thedirection of said acceptor substrate.
 22. The method of claim 20,wherein said energy source is computer controlled with respect to on-offmodes of operation.
 23. The method of claim 1, wherein said energysource is disposed at a point within a hollow cylindrical roller havingan inner and an outer surface; wherein said donor substrate is a firstrigid or flexible material sheet having said small molecule organicsemiconductor layer thereon; wherein said acceptor substrate is a secondrigid or flexible material sheet, wherein said first and said secondmaterial sheets are passed simultaneously between said hollowcylindrical roller and a second roller, said rollers being in contactwith one another along their longitudinal axes to permit saidsublimation and said deposition of said small organic molecule from saidfirst material sheet to said second material sheet.
 24. A substratehaving thereon a patterned small molecule organic semiconductor layercomprising: a small organic molecule sublimed and deposited by exposinga donor substrate having thereon a small molecule organic semiconductorlayer to energy.
 25. A system for producing a substrate having thereon apatterned small molecule organic semiconductor layer comprising: a donorsubstrate having thereon a small molecule organic semiconductor layer;an acceptor substrate positioned to receive said patterned smallmolecule organic semiconductor layer upon exposing said donor substrateto energy; and an energy source to produce said energy to cause thesublimation and deposition of a small organic molecule onto saidacceptor substrate.
 26. The system of claim 25, further comprising: anenergy absorbing film interposed between said donor substrate and saidsmall molecule organic semiconductor layer to absorb said energy andcause thermal transfer of said small organic molecule.
 27. The system ofclaim 25, wherein said small molecule organic semiconductor layer isproduced by at least partial conversion of a precursor of the smallorganic molecule during said exposing of said donor substrate.
 28. Thesystem of claim 27, further comprising: a heating source to anneal saidacceptor substrate after said deposition of said patterned smallmolecule organic semiconductor layer on said acceptor substrate, whereinsaid annealing is at about the thermal decomposition temperature of saidprecursor to convert any remaining precursor to said small organicmolecule.
 29. The system of claim 25, further comprising: means forrelatively moving said donor substrate, said acceptor substrate, saidenergy source, or a combination thereof.
 30. The system of claim 25,further comprising: a mask, wherein said mask is interposed between saiddonor substrate and said acceptor substrate.
 31. The system of claim 25,wherein said donor substrate is a rigid or flexible ribbon.
 32. Thesystem of claim 31, wherein said ribbon is part of a reel to reelapparatus.
 33. The system of claim 25, wherein said donor substrate is adisk mounted on a rotatable axis.
 34. The system of claim 25, whereinsaid donor substrate is in the shape of a hollow cylindrical rollerhaving an inner and an outer surface, said outer surface having thereonsaid small molecule organic semiconductor layer.
 35. The system of claim25, wherein said energy source is disposed at a point within a hollowcylindrical roller having an inner and an outer surface; wherein saiddonor substrate is an optically transparent first rigid or flexiblematerial sheet having an energy absorbing film interposed between saiddonor substrate and said small molecule organic semiconductor layer;wherein said acceptor substrate is a second rigid or flexible materialsheet, wherein said first and said second material sheets are passedsimultaneously between said hollow cylindrical roller and a secondroller, said rollers being in contact with one another along theirlongitudinal axes to permit said sublimation and said deposition of saidsmall organic molecule from said first material sheet to said secondmaterial sheet.